A long-running public feud between members of Sir Edmund Hillary's family has come to a head with the resignation of his widow as chair of the charity the Everest hero set up to help the sherpas of Nepal.

The decision by Lady June Hillary and five other board members to quit the Himalayan Trust is the latest – and perhaps last – skirmish between the mountaineer's second wife and the surviving children of his first marriage, Peter and Sarah.

Lady June had been a board member since the charity was established in 1966.

She said she had reached the decision during the 50th anniversary celebrations of Khumjung School in Nepal's Solu-Khumbu district, the first project Sir Edmund built to help the Sherpas. "Things had changed," she said. "I had done enough."

The mass resignation from the Himalayan Trust's board follows last year's bitter argument over the ownership of several Rolex watches, including one awarded to Sir Edmund after the first ascent of Everest in 1953.

When Lady June tried to sell the watches through the Swiss auction house Antiquorum, Peter and Sarah sought court orders to prevent her going ahead with the sale.

The New Zealand government also intervened, warning that under the country's heritage laws, the Everest watch should not have been allowed to leave the country.

When the courts awarded ownership of the watches to Sir Edmund's children, Peter promised to donate them to the Auckland War Memorial Museum.

Mary Lowe is the secretary of the Himalayan Trust's sister organisation in the UK, and married to Everest veteran George Lowe, the New Zealand climber who shared many of Sir Edmund's best adventures.

"We can't hide the fact that Peter and June never got on," she told the Guardian. "They're both tough characters. June's been working for the Himalayan Trust for 50 years. It's just the right moment for her. It's a new start."

The origins of the feud lie in Sir Edmund's dramatic life story. In 1975, his first wife Louise and his younger daughter Belinda were killed in a light aircraft crash as they flew from Kathmandu to meet him in the mountain village of Phaplu, where his Himalayan Trust team were building a hospital.

In 2005, Sarah told her father's biographer Alexa Johnston that those in the family best able to cope with such a tragedy were those who had died. The survivors, she said "spun off in our individual directions".

Sir Edmund credited Lady June for drawing him out of the depression he suffered following the tragedy. They had both been widowed when they married in 1989.

Lady June's first husband, the climber and yachtsman Peter Mulgrew, a longstanding friend of Sir Edmund's, died in 1979 when a sightseeing plane to Antarctica crashed into Mount Erebus.

Mulgrew had replaced Sir Edmund as the flight's celebrity commentator.

Peter, 56, followed his father into adventuring, climbing Everest twice and travelling to the south pole, doing his own share of philanthropic work as a director of the Australian Himalayan Foundation.

After Sir Edmund's death, Lady June blocked a suggestion from board member Dr Michael Gill that Peter should be brought in.

Gill, who recently published Himalayan Hospitals, an account of the Himalayan Trust's work, said that the feud over the watches was sparked by the struggle over the charity's future direction. That struggle now seems over.

The Himalayan Trust, with just four board members still in post, including Sarah, issued a statement thanking Lady June for five decades of work, while promising to begin a series of reforms and find new leadership for the charity.

"It's a good thing," said Mary Lowe. "It will be more democratic, people will serve limited terms."

Lowe says she hopes attention can now return to the work of the charities around the world that Sir Edmund inspired, including the Himalayan Trust.

The epicentre of the deadly earthquake that struck the Himalayas in September was close to Kangchenjunga, the world's third-highest mountain.

Himalayan Trust UK funds several schools in the region, eight of which were damaged or destroyed.

Lowe said that Nepal's failing state education sector "has made the trust's teacher-training work more important than ever".